Does anyone know if removing the stock 2" block and replacing it w/a 4" block cause me to extend my driveshaft or lower my transmission? Will this mean I am actually doing a 2" or 4" lift? I was wondering if the stock 2" block has already pulled out the driveshaft slightly from the tailhousing and 2 inches more might completly disengage the driveshft from the transmission.

Background: I have a 3 inch BDS AAL which is in an "offroad" spring pack which gives me almost 5 inches of lift over a stock ram. I use the factory block.

I have no issues with my driveshaft, although it does stick out of the tailshaft about 3/4 inch more than stock.
A 4 inch block will lift your rear axle about 2 inches.
I'm not a fan of taller blocks or stacking blocks. Because of the direction the pinion moves under acceleration (upward). Taller or stacked blocks create a longer leverage point. This can cause or increase axle wrap which can lead to wheel hop under accelleration and braking.
Add a leafs (AAL) while more difficult to install, bend your stock springs to create lift. While this can lead to a much firmer ride, it also avoids the pitfalls of blocks.
IMO..."long style" AALs are the best choice. Short AALs are way too stiff. They can cause spring damage and give a VERY harsh ride.

EDIT: Eventually your new front springs will settle enough to level out the truck.